The present invention pertains to apparatus and methods for preparing a sample such as a biological or pathologic sample for further examination by separating solids such as solid tissues from liquids contained in the sample.
Certain biological and pathological procedures require treatment of samples including solid tissues and a liquid phase, in order to remove the liquid phase. For example, such treatment is required in certain pathological staging procedures. The pathologic stage is a piece of diagnostic information relating to whether cancer has spread or “metastasized” in a patient having or suspected of having cancer. The pathologic stage is used in determining the patient's prognosis and treatment, including whether or not the patient will receive chemotherapy. Colorectal cancer typically metastasizes first to lymph nodes disposed in fatty tissue in the abdomen. Thus, examining these lymph nodes and adjacent fibrous tissue provides important information useful in determining the stage of colorectal cancer.
To determine the pathologic stage of colorectal cancer, the surgeon first resects a section of fatty tissue from the patient's abdomen. This fatty tissue is then sent to the surgical pathologist, whose responsibility is to determine the stage of the illness based on the extent of cancer observed within this tissue. Importantly, the pathologist is not interested in the fat itself, but rather in the fibrous tissue and lymph nodes that are contained within the fatty tissue.
In traditional staging methods, the pathologist meticulously dissects the fatty tissue with a scalpel in search of fibrous material and lymph nodes. The pathologist removes any clearly visible nodes or other relevant fibrous tissue for examination under the microscope. Inevitably, however, some very small or microscopic pieces of tissue are left behind. The presence or absence of any diagnostically relevant information (which may be microscopic) within the resected tissue may change the patient's prognosis and treatment. To account for this, the pathologist conventionally selects five to ten random samples from the tissue for microscopic study.
In recent years, a team of pathologists in Germany has pioneered a sample preparation technique that makes this process both more efficient and more accurate. This method is referred to as the “acetone compression method” or “ACM.” The ACM is described in Gehoff et al., Am. J. Surg. Pathol., Vol. 36, pp. 202-213, 2012; Basten et al., Pathologe, Vol. 31, pp. 218-224, 2010; and Scheel et al., “Comprehensive lymph node morphometry in rectal cancer using acetone compression”, J. Clin. Pathol., e-published Mar. 16, 2015, the disclosures of which are hereby incorporated by reference herein. The ACM allows the pathologist to eliminate the time-consuming dissection process while simultaneously avoiding the risk of missing diagnostically relevant tissue.
In practice of ACM, the pathologist first examines the fatty tissue sample for any large and clearly visible pieces of diagnostically relevant tissue. The pathologist then slices the sample into small (2 to 3 mm) sections and puts this material in acetone to soak overnight. Acetone dissolves lipids without affecting the integrity of fibrous tissue. The following day, the tissue is removed from the acetone bath. The sample as removed includes the tissue of interest together with acetone having lipids dissolved therein. This sample is loaded into a metal tube having a circumferential wall that is perforated with small (1 to 2 mm diameter) holes. The pathologist places the tube in an arbor press. The arbor press includes a lever linked through a rack and pinion mechanism to a ram. By pulling the lever manually, the pathologist forces the ram into the tube through one end while the other end of the tube is blocked, thereby compressing the sample in the tube. Compressing the sample forces the liquid phase including the fatty components to be extruded out of the small holes in the tube, leaving the solid components, including the fibrous tissue and lymph nodes in the tube. The pathologist has therefore reduced or eliminated diagnostically irrelevant information, i.e. fat, from the tissue sample. The solid tissue, and particularly the lymph nodes, is then examined by the pathologist to determine the presence or absence of metastases. Such examination may include, for example, morphological examination of the lymph nodes and microscopic examination after further processing such as sectioning and staining using known techniques. For accurate staging, it is desirable to examine a large number of lymph nodes.
ACM represents a more time-efficient approach for processing the tissue than conventional hand dissection. In addition, ACM eliminates the risk that the pathologist may overlook diagnostically relevant information, therefore increasing the accuracy of the pathologic staging process for cancers of this type. ACM is capable of providing double or even quadruple the number of lymph nodes, compared to the conventional technique of tedious dissection.
However, still further improvement would be desirable.